War Pass, a Breeders' Cup winner, has died in mysterious circumstances less than 24 hours after returning to his United States stud from a second Australian shuttle season.Lane's End Farm, the famous US thoroughbred nursery, said the stallion was found dead in his Kentucky paddock."We are very saddened to lose such a promising young stallion," Lane's End Farm's William Farish said.The cause of the five-year-old's death is unknown with preliminary autopsy results proving inconclusive.War Pass was

War Pass, a Breeders' Cup winner, has died in mysterious circumstances less than 24 hours after returning to his United States stud from a second Australian shuttle season.

Lane's End Farm, the famous US thoroughbred nursery, said the stallion was found dead in his Kentucky paddock.

"We are very saddened to lose such a promising young stallion," Lane's End Farm's William Farish said.

The cause of the five-year-old's death is unknown with preliminary autopsy results proving inconclusive.

War Pass was retired to Lane's End Farm with a record of five wins from seven starts and more than $US1.5 million in earnings.

A two-time Group One winner, War Pass' defining racetrack moment came with his Breeders' Cup Juvenile triumph in the Monmouth Park mud in 2007.

He stood two seasons at stud and has foals on the ground in both the northern and southern hemispheres.

By Cherokee Run from the Mr Prospector mare Vue, War Pass shuttled twice to Australia to stand at Widden Stud in the Hunter Valley in NSW.

"He had everything we look for in a sire and was potentially the sort of outcross horse we really need down here, so we were shocked and bitterly disappointed to learn of his premature death," Widden's Antony Thompson said in a statement.